LAUSR

Exploring van der Waals heterostructures (vdWHs) based on two-dimensional (2D) materials is of importance for designing new materials or tuning the properties of existing materials. By virtue of first-principles calculations, we propose a type-I vertical 2D α-tellurene/Ca(OH)2 vdWH with an indirect bandgap of 1.10 eV, in which both the CBM and VBM originate completely from tellurene. In addition, we also show that such a vdWH presents excellent optical absorption and an unexpectedly hyperbolic nature, which is mainly determined by tellurene. Hyperbolic materials play a central role in nanophotonics. In tellurene and Te-based materials, we for the first time report this natural hyperbolic property, which was previously unknown. More importantly, under in-plane biaxial strain or vertical strain, the α-tellurene/Ca(OH)2 bilayer transforms into a direct bandgap type-II vdWH, in which both the CBM and VBM located at the Γ point are contributed by the tellurene and Ca(OH)2 monolayers, respectively. Meanwhile, the application of strain can also be used to tune the optical absorption and the frequency range of the hyperbolic property. Our findings extend the applications of tellurene and Te-based vdWHs in nanodevices and provide some guidance for investigating the related vdWHs.